Jale Hacaloglu

Functional Electrospun Polystyrene Nanofibers Incorporating α-, β-, and γ-Cyclodextrins: Comparison of Molecular Filter Performance

Electrospinning has been used to successfully create polystyrene (PS) nanofibers containing either of three different types of cyclodextrin (CD); α-CD, β-CD, and γ-CD. These three CDs are chosen because they have different sized cavities that potentially allow for selective inclusion complex (IC) formation with molecules of different size or differences in affinity of IC formation with one type of molecule. The CD containing electrospun PS nanofibers (PS/CD) were initially characterized by scanning electron microscopy (SEM) to determine the uniformity of the fibers and their fiber diameter distributions. X-ray photoelectron spectroscopy (XPS) was used to quantitatively determine the concentration of each CD on the different fiber surfaces. Static time-of-flight secondary ion mass spectrometry (static-ToF-SIMS) showed the presence of each type of CD on the PS nanofibers by the detection of both the CD sodium adduct molecular ions (M + Na+) and lower molecular weight oxygen containing fragment ions. The comparative efficiency of the PS/CD nanofibers/nanoweb for removing phenolphthalein, a model organic compound, from solution was determined by UV-vis spectrometry, and the kinetics of phenolphthalein capture was shown to follow the trend PS/α-CD > PS/β-CD > PS/γ-CD. Direct pyrolysis mass spectrometry (DP-MS) was also performed to ascertain the relative binding strengths of the phenolphthalein for the CD cavities, and the results showed the trend in the interaction strength was β-CD > γ-CD > α-CD. Our results demonstrate that nanofibers produced by electrospinning that incorporate cyclodextrins with different sized cavities can indeed filter organic molecules and can potentially be used for filtration, purification, and/or separation processes.

Electrospinning of functional poly(methyl methacrylate) nanofibers containing cyclodextrin-menthol inclusion complexes

Electrospinning of nanofibers with cyclodextrin inclusion complexes (CD-ICs) is particularly attractive since distinct properties can be obtained by combining the nanofibers with specific functions of the CD-ICs. Here we report on the electrospinning of poly(methyl methacrylate) (PMMA) nanofibers containing cyclodextrin-menthol inclusion complexes (CD-menthol-ICs). These CD-menthol-IC functionalized nanofibers were developed with the purpose of producing functional nanofibers that contain fragrances/flavors with high temperature stability, and menthol was used as a model fragrance/flavor material. The PMMA nanofibers were electrospun with CD-menthol-ICs using three type of CD: alpha-CD, beta-CD, and gamma-CD. Direct pyrolysis mass spectrometry (DP-MS) studies showed that the thermal evaporation of menthol occurred over a very high and a broad temperature range (100-355 degrees C) for PMMA/CDmenthol-IC nanowebs, demonstrating the complexation of menthol with the CD cavity and its high temperature stability. Furthermore, as the size of CD cavity increased in the order alpha-CD<beta-CD<gamma-CD, the thermal evolution of menthol shifted to higher temperatures, suggesting that the strength of interaction between menthol and the CD cavity is in the order gamma-CD>beta-CD>alpha-CD.

Characterization of degradation products of polyethylene oxide by pyrolysis mass spectrometry

Abstract The techniques of direct and indirect (evolved gas analysis) pyrolysis MS are used to characterize the thermal degradation products of polyethylene oxide. Using direct pyrolysis MS technique the main degradation process is determined to be due to CO and CC scissions yielding fragments characteristic of the polymer. Evolved gas analysis indicates formation of small molecular stable compounds such as C 2 H 5 OC 2 H 5 , CH 3 CHO, CO 2 , CO and C 2 H 4 .

The formation and characterization of cyclodextrin functionalized polystyrene nanofibers produced by electrospinning

Polystyrene (PS) nanofibers containing the inclusion complex forming beta-cyclodextrin (beta-CD) were successfully produced by electrospinning aimed at developing functional fibrous nanowebs. By optimization of the electrospinning parameters, which included varying the relative concentration of PS and beta-CD in the solutions, bead-free fibers were produced. Homogeneous solutions of beta-CD and PS in dimethylformamide (DMF) were used with concentrations of PS varying from 10% to 25% (w/v, with respect to DMF), and beta-CD concentrations of 1% to 50% (w/w, with respect to PS). The presence of beta-CD facilitated the production of bead-free PS fibers even from lower polymer concentrations as a result of the higher conductivity of the PS/CD solutions. The morphology and the production of bead-free PS/CD fibers were highly dependent on the beta-CD contents. Transmission electron microscope (TEM) and atomic force microscope (AFM) images showed that incorporation of beta-CD yielded PS fibers with rougher surfaces. Thermogravimetric analysis (TGA) and direct insertion probe pyrolysis mass spectroscopy (DP-MS) results confirmed the presence of beta-CD in the PS fibers. X-ray diffraction (XRD) spectra of the fibers indicated that the beta-CD molecules are distributed within the PS matrix without any phase separated crystalline aggregates up to 40% (w/w) beta-CD loading. Furthermore, chemical analyses by Fourier transform infrared (FTIR) spectroscopy studies confirm that beta-CD molecules are located within the PS fiber matrix. Finally, preliminary investigations using x-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-static-SIMS) show the presence of the cyclodextrin molecules in the outer molecular layers of the fiber surfaces. The XPS and ToF-SIMS findings indicate that cyclodextrin functionalized PS webs would have the potential to be used as molecular filters and/or nanofilters for the purposes of filtration/purification/separation owing to surface associated beta-CD molecules which have inclusion complexation capability.

PYROLYSIS MASS SPECTROMETRIC ANALYSIS OF STYRENE-BUTADIENE BLOCK AND RANDOM COPOLYMERS

Direct pyrolysis mass spectrometric analysis of a styrene-butadiene-styrene block copolymer indicated that thermal decomposition of each block shows a resemblance to the related homopolymer, giving a possibility of differentiation of blocks. However, the random analog, the styrene butadiene rubber, degraded in a manner that is somewhat in between in nature of the thermal characteristics of both homopolymers. This technique shows promise to differentiate thermal behaviors of each sequence in block polymers if any exist. Indirect pyrolysis mass spectrometric analysis gave no clear evidence for differentiation of the nature and the composition of the copolymers.

Spectroscopic investigation of oxidation of p-toluene sulfonic acid doped polypyrrole

Abstract Oxidative degradation of electrochemically synthesized p -toluene sulfonic acid doped polypyrrole, PTS-PPY was studied by the application of evolved gas analysis using IR spectroscopy and direct insertion probe pyrolysis mass spectrometry techniques. It has been observed that PPY films prepared in aqueous media contained high concentration of oxygenated species even if the synthesis potential was kept low. The extent of overoxidation associated to ketone formation increased by increasing the applied potential and thermal ageing. The decrease in conductivity is attributed to the replacement of dopant, as a result of nucleophlic attack on the polycationic chain, by hydroxide and/or O 2 . Pyrolysis analyses also indicated that chemically prepared samples were oxygenated in air more readily and yielded mainly CO groups. Presence of hydroxide groups for these samples may be associated with the adsorption of H 2 O in air or H 2 O present during synthesis as an impurity. The direct insertion probe pyrolysis mass spectrometry technique was shown to be a very powerful technique for not only determining the thermal decomposition products but a investigating the interaction of dopant and oxygenated species with the polymer matrix.

Thermal decomposition of glycidyl azide polymer by direct insertion probe mass spectrometry

Abstract Thermal decomposition reactions and products of glycidyl azide polymer (GAP), have been investigated by direct insertion mass spectrometry and evolved gas analyses by FTIR spectroscopy techniques. It has been observed that thermal degradation of GAP begins with cleavage of the side groups. Although the main decomposition started with the elimination of molecular nitrogen from the azide functional group, degradation initiated by loss of N 3 and CH 2 N 3 , depolymerization type reactions were also identified. Rearrangement reactions and/or H 2 evolution after the initiation step resulted in various polymeric structures that decompose subsequently. Furthermore, loss of low molecular weight, stable species such as CH 3 N 3 and HN 3 directly from GAP and H 2 CNH, and HCN from polymeric imine produced by the rearrangement reactions following elimination of N 2 from GAP have shown to be effective. Evolved gas analyses by FTIR spectroscopy confirmed formation of small molecular weight species such as CO, CH 4 , C 2 H 2 , CH 2 CO, and NH 3 .

Conducting polymer composites of polythiophene with natural and synthetic rubbers

Electrochemical synthesis of conducting polymer composites of polythiophene was achieved. Synthetic and natural rubbers were used as the insulating polymer matrices. FT-IR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mass spectrometry (MS) were utilized to characterize the composite blends. The conductivity measurements were done by using a standard four-probe technique. The above-mentioned methods show that the resultant composites have different properties compared to polythiophene due to interaction of the rubbers with electrochemical polymerization of thiophene, whereas the same argument is not valid for the polypyrrole synthesis via the same procedure.

Characterization of electrochemically synthesized p-toluene sulfonic acid doped polypyrrole by direct insertion probe pyrolysis mass spectrometry

Abstract A direct insertion probe pyrolysis mass spectrometry technique was used to perform a systematic thermal characterization of conducting polypyrrole doped with p -toluene sulfonic acid. The effect of dopant concentration on thermal stability and degradation products was investigated using undoped and dedoped polypyrrole samples. The data indicate that polymerization of pyrrole in the absence of dopant produces an aromatic structure, which transforms into the quinoid form at high dopant concentrations. Reduction, namely dedoping, yielded a decrease in the intensity of PTS based peaks and transformation from quinoid form to aromatic form. Intense toluene, SO 2 , and H 2 S peaks recorded at high temperatures indicated the decomposition of the dopant. This trend, decomposition at high temperatures instead of evaporation at low or moderate temperatures was associated with a strong (probably chemical) interaction between the dopant and the host polymer.

Pyrolysis mass spectrometric analysis of styrene–isoprene–styrene copolymer

Abstract Thermal analysis of styrene–isoprene–styrene block copolymer, using the direct pyrolysis mass spectrometry (MS) technique, indicated that each block showed very similar thermal behavior with the corresponding homopolymer. The isoprene block was found to be thermally less stable, decomposing by random scissions followed by cyclization reactions. The more stable styrene block degraded by a radical depolymerization mechanism. With an indirect pyrolysis MS technique, it was found that production of benzene, toluene, 1-methyl cyclopentene and 1-methyl cyclohexene was more effective when degradation was carried out in a closed reactor.